All aircraft are equipped with altimeters which have various degrees of sophistication. The smaller aircraft that are generally flown for recreation as well as for business have the most unsophisticated instrumentation. Generally, the altimeter in most light aircraft is a simple barometric device which senses altitude by the linear expansion of an evacuated metal bellows fastened to a gear train that revolves a pointer. As the aircraft rises, the external pressure decreases and the evacuated metal bellows expands outward correspondingly. These altimeters may be compensated to account for the ambient temperature and are usually adjustable by the pilot to compensate for local barometric pressure. Much more complicated altitude sensing devices are used on larger aircraft but the majority of light aircraft use simple systems similar or identical to the one described above.
When a pilot flies an aircraft he constantly monitors the altitude for a number of reasons, all having to do with safety. In controlled airways, the FAA assigns distinct altitudes to aircraft and these altitudes depend on the compass heading of the individual aircraft. This assignment, known by all pilots, prevents collisions by aircraft which may be occupying or crossing over the same geographic location at the same time. Also, aircraft flight controllers may assign a particular altitude and heading to an individual aircraft so as to prevent collisions and to assure safety. In addition, it may be necessary to fly above a minimum height to avoid collision with mountains, buildings and structures such as radio towers etc.
The pilot should be able to improve the safety of flying if he could devote his visual senses more fully to other instruments, to keeping a better watch for other aircraft and for navigation. This is especially the case at night and while flying under instrument or marginal conditions and when in busy airspace near an airport.
Therefore, it is the object of this invention to relieve the pilot of the constant necessity of monitoring the altimeter once he has reached an acceptable altitude. The inventors have built and tested a number of different models of this invention and have found that the aircraft pilot can take this portable self-contained invention with him on any aircraft and use it in conjunction with the aircraft's built in altimeter to reduce the instrument monitoring requirements.
These and other objects and advantages attained by the invention will become more fully apparent in the description of a preferred embodiment of the invention which follows below.